1. Field of the Invention
This invention relates generally to ceramic dielectric compositions which have dielectric constants (K) of 60 to about 140, dissipation factors (DF) less than 0.1 percent, and temperature coefficient characteristics (TCC) from about -20 ppm to about -1000 ppm/.degree.C. The TCC characteristics meet different designations as described in EIA RS198C specification.
2. The Prior Art
Multilayer ceramic capacitors are commonly made by casting or otherwise forming insulating layers of dielectric ceramic powder; placing thereupon conducting metal electrode layers, usually a palladium/silver alloy in the form of metallic paste; stacking the resulting elements to form the multilayer capacitor; and firing to densify the material thus forming a multilayer ceramic capacitor. Prior art multilayer ceramic capacitors suffer from the disadvantage that they do not exhibit low dissipation factors and predictable capacitance change per degree C. temperature change (TCC) characteristics with respect to their room temperature values. Such characteristics are required in electronic circuit applications such as timing circuits, resonator circuits, or TV tuner circuits.
It would be desirable for dielectric ceramic compositions used in multilayer capacitors for the aforementioned applications to have a stable dielectric constant over a wide temperature range. For example, the dielectric constant should change from its base value at 25.degree. C. (room temperature) per degree C. temperature change (TCC) by not more than -1000 ppm/.degree.C. This change also should be linear and predictable. The insulation resistance times capacitance product of such compositions should be more than 1000 ohm-farads at 25.degree. C. and more than 100 ohm-farads at maximum working temperatures, 125.degree. C. in most cases. Also the dielectric constants (K) should be as high as possible and the dissipation factors (DF) should be as low as possible.